Important issues for designing the multiple antenna transmission apparatus are diversity gain and reception complexity. One of methods for getting the maximum diversity gain is the Alamouti transmission method.
The signal transmission apparatus according to the Alamouti transmission method includes two antennas, and has a transmission efficiency of 1. As the signal transmission apparatus according to the Alamouti transmission method has the maximum diversity gain and low reception complexity, it is widely used. However, if the signal transmission apparatus according to the Alamouti transmission method has 3 or more antennas, it does not have a transmission efficiency of 1 for the maximum diversity gain and low reception complexity. Also, the signal transmission apparatus has large reception complexity for the maximum diversity gain and the transmission efficiency of 1.
To resolve this problem, a method (‘IEEE802.16e/D12, Part 16: Air interface for fixed and mobile broadband wireless access systems’, October 2005, p. 473-474) of using two Alamouti Blocks such as in Equation 1 has been disclosed.
                    (                                                            s                1                                                                    -                                  s                  2                  *                                                                    0                                      0                                                                          s                2                                                                    s                1                *                                                    0                                      0                                                          0                                      0                                                      s                3                                                                    -                                  s                  4                  *                                                                                        0                                      0                                                      s                4                                                                    s                3                *                                                    )                            [                  Equation          ⁢                                          ⁢          1                ]            
In the matrix of Equation 1, symbols of each row mean symbols transmitted to different antennas respectively, symbols of the first row and the third row mean symbols transmitted at a time k, and symbols of the second row and the fourth row mean symbols transmitted at a time k+1. The first Alamouti block consisting of the first row and the second row and the second Alamouti block consisting of the third row and the fourth row are transmitted through different orthogonal resources (or subcarriers).
However, the signal transmission apparatus according to the method such as Equation 1 has a loss of diversity gain for low reception complexity and a transmission efficiency of 1. Also, the method such as Equation 1 is not suitable for a signal transmission apparatus with 3 or 5 antennas.